The present invention relates to a passenger conveyor and more particularly to a safety device for a passenger conveyor which operates to issue an alarm or to stop the operation of the conveyor when there arises any deviation between the speed of the tread boards on which the passenger rides and the speed of the handrails of the conveyor.
First, an example of the hitherto publicly known safety devices of this kind will be explained. Japanese Laid-Open Patent Publication No. 135084 discloses a safety device as illustrated in FIG. 1 of the accompanying drawings wherein the main frame 1 of a passenger conveyor is provided at its upper and lower end portions with a driving means 2 and a tension means 3, respectively, and endless tread board chains 4 are reeved on the sprockets mounted on the driving means 2 and the tension means 3, respectively. A number of tread boards 5 are continuously pivotally connected to the endless tread board chains 4, and endless handrails 6 are arranged along the tread boards 5 so as to be circulatingly driven. The handrail 6 is driven by driving pulleys 7 which are in contact therewith, thrust rollers 8 to thrust up the handrail 7, a transmission roller 10 driven by the driving means 2 through an endless handrail driving chain 9, and endless belts 11 reeved on the transmission roller 10 and the driving pulleys 7. In FIG. 1, the reference numeral 12 designates a tension means to apply tension to the handrail 6, 13 designates a velocity detector in contact with the handrail 6 to detect its velocity, and 14 designates a velocity detector mounted on the driving means 2 to detect the velocity of the tread boards 5.
The purpose of these detectors 13 and 14 is as follows.
In a passenger conveyor, in order to ensure the safety of the passenger, it is necessary to synchronize the speeds of the tread boards 5 and the handrails 6, but although the speed of the tread boards 5 is kept constant, the speed of the handrails 6 has a tendency to be gradually decreased due to a decrease in friction between the driving pulleys 7 and/or elongation of the handrails 6, since the latter are driven by frictional contact with the driving pulleys 7. Therefore, the velocities of the tread boards 5 and the handrails 6 are continuously detected by the detectors 14 and 13, respectively, and upon detection of any difference in the velocities, an alarm is issued or the passenger conveyor is caused to be stopped.
However, as will be understood from the above explanation, in this example of a conventional safety device, since the velocities of the tread boards 5 and the handrails 6 are separately detected by the detectors 14 and 13, respectively, and since they have to be compared with each other, in addition to the velocity detectors a comparison device to compare the two velocities is necessary, making the arrangement complicated.
Further, since the velocity detector 13 to detect the velocity of the handrails 6 detects the velocity by the rate of rotation of a roller which is in frictional contact with the handrails 6, there can arise a change in the rate of rotation of the roller due to any decrease in the frictional force between them, preventing the detection of the correct velocity.
Although a lag in the velocity of the handrails 6 relative to the velocity of the tread boards 5 is to some extent permissible, in the conventional safety device as above exemplified the comparison of the difference in the two velocities with a predetermined permissible velocity difference is difficult. As a result, there arise troubles such as the safety device being actuated even when the velocity difference is still within the predetermined permissible difference.
As another example of a safety device for a passenger conveyor, Japanese Laid-Open Utility Model Publication No. 3175/1981 discloses one wherein separate idle rollers are provided so as to be in contact with the handrails as well as with the handrail driving rollers and the difference in the speeds of the idle rollers is detected by a mechanical mechanism.
However, it will be apparent that this safety device has defects similar to those possessed by the first example.